Open-File Report 83-778

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Abstract

Crone electromagnetic, self-potential, and induced polarization surveys were conducted in the Dhahar-Al Hajrah region, southwestern Saudi Arabia, in support of geological and geochemical exploration for volcanogenic sulfide deposits. Although a previous, airborne electromagnetic survey found no anomalies in the vicinity of the ancient mines in the region, surface indications of anomalous copper and zinc at both Dhahar and Al Hajrah are abundant.
Reconnaissance Crone electromagnetic traverses across the Dhahar prospect area delineated numerous conductive zones, but none had a dip-angle anomaly of more than 10?. Similar results were obtained at Al Hajrah.
With one or two encouraging exceptions, self-potential surveys at Al Hajrah showed only broad gradients and anomalies having amplitudes of less than 40 mV. Dipole-dipole induced polarization surveys at Al Hajrah delineated two nearly continuous polarizable zones having an aggregate strike length of almost 7 km. The two zones are symmetrically disposed on either side of a median aplitic dike and may lie on opposing limbs of a south-plunging antiform. Chargeabilities in the anomalous zones are weak to moderate but in most places are clearly associated with anomalous copper and (or) zinc concentrations found by surface sampling.
Ground electromagnetic traverses are recommended to determine the most conductive intervals of anomalous induced polarization effect in the anomalous zones; these conductive intervals should then be tested by drilling, where appropriate. Reconnaissance self-potential traverses are also recommended at Dhahar, and additional ground electromagnetic surveys are recommended across two airborne electromagnetic anomalies located immediately southeast of the Al Hajrah target.

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